Consumers like foam producing products for a variety of personal and cleaning uses, such as laundry detergents, hand dish washing liquids, hard surface cleaners, hair and body shampoos, facial cleansers, shave preparation gels, and dentifrices. Foam based cleaning products create less mess and foam based personal care products have a pleasant feel. Consumers particularly like high and thick foams, quick foaming action, lasting foams, and the feel of rich, luxurious, creamy foams. To achieve these desirable effects, surfactants are added to many cleaning and personal care products. Surfactants play a major role in foam producing products by lowering the dynamic surface tension of the liquid-air interface to allow gas bubbles to be formed or introduced beneath the surface of the liquid. Surfactants also stabilize the foam once it is formed. However, surfactants are not without disadvantages.
The addition of surfactants adds to the cost of the final product. Further, there are environmental concerns associated with heavy use of some surfactants. Therefore, it is desirable to reduce the amount of surfactant in foam producing products, but without loss of the beneficial foaming properties surfactants offer.
The effect of particles on foamed products as reported in the literature has been inconsistent. Fine particles are known to be able to generate foams in the absence of a surfactant, probably by coating air bubbles and thereby minimizing interfacial fluid energy. However, some particles, such as hydrophobic famed silica in aggregate form of about 200 to 300 nm, are reported to function as defoaming agents.
U.S. Pat. No. 6,586,483 describes a foaming composition comprised of surface-modified, non-aggregated, inorganic nanoparticles, such as silica and titania, having a particle diameter of less than about 100 nm disposed in a vehicle, such as water or an organic liquid, with or without surfactant.
A foaming composition for use in cleansing the skin is described in U.S. Pat. No. 6,894,012. The composition contains at least one nonionic, anionic, amphoteric or zwitterionic foaming surfactant, 1% or more of silica particles of about 3 to 50 nm, an oxyalkylenated compound and one or more of a cationic or amphoteric polymer.
While high and thick foams are desirable, they have heretofore been difficult to rinse away without the use of excessive amounts of water or other rinse liquid. There is a tension between the desire for foaming products with good foam yield and the need to effectively rinse away the foam and avoid wasting water. In some areas of the world and at various times during the year, water conservation is of paramount importance.
The effect of fine particles in surfactant-based systems on foam generation and stability has not been fully elucidated in the literature. There does not appear to be any general understanding of how fine solid particles interact with surfactants during the process of foam generation.